The present invention relates to a thermally insulated engine including a combustion chamber, principal portions of which are made of a thermally insulating material.
There has been developed a thermally insulated engine including heated portions around a combustion chamber, such as a cylinder liner, a cylinder head, a piston head, piston rings, valves, and intake and exhaust ports, which are made of a ceramic material as a thermally insulating material.
With such a thermally insulated engine, the cylinder liner and the cylinder head are not required to be cooled, and hence a radiator system therefor is not necessary. Since the engine itself is structurally simple, it is much lighter and smaller in volume than conventional engines.
However, inasmuch as the cylinder liner and the cylinder head are not cooled, the inner wall surface of the combustion chamber is kept at a high temperature when the thermally insulated engine is subjected to a full load. Stated otherwise, when the engine is operated for acceleration, the air which is adiabatically compressed is heated to a high temperature and kept under a high pressure at the end of the compression stroke. Therefore, more nitrogen oxides (NOx) tend to be produced when the fuel is burned than they are in the combustion chamber of an engine which has an ordinary radiator.
In order to suppress the generation of nitrogen oxides, the fuel may be supplied at an increased rate for an increased air-fuel ratio. If the air-fuel mixture becomes rich, however, soot (black smoke) is produced.